1. Field of the Invention
The present invention relates to a content distribution system, a description data distribution apparatus, a content location management apparatus, a data conversion apparatus, a reception terminal apparatus and a content distribution method, which distribute multimedia contents (such as, audio data and video data).
2. Description of the Related Art
In recent years, the Internet has become popularized. As a result, various contents have been transmitted/received between communication terminal apparatus over the Internet. Particularly, broadband access links has become possible through the birth of ADSL, FTTH, and IMT-2000. Accordingly, distribution of high capacity multimedia contents (such as, audio data, and video data) has been realized.
FIG. 1 is a diagram illustrating the configuration of a conventional multimedia content distribution system. The distribution system includes a first distribution apparatus 21 (SMIL data distribution apparatus) storing multimedia content description data. The first distribution apparatus 21 transmits the data to a reception terminal apparatus 23. The distribution system includes a second distribution apparatus (content distribution apparatus) 22 that distributes multimedia contents to a reception terminal apparatus 23; the reception terminal apparatus 23 that receives and replays the multimedia contents; and a network 20 that links each of the apparatus.
For example, the multimedia content description data is data that includes, in a predetermined language, the location information (such as, an IP address or an URL) of apparatus in which multimedia contents exist, layout information, and time information (such as time information concerning synchronization timing of audio and video data and display timing of audio and video data). An example of this a predetermined language may include Synchronized Multimedia Integration Language (SMIL).
FIG. 2 is a diagram showing an exemplary description of SMIL (an example of multimedia content description data). In FIG. 2, the portion (such as, the portion [<region id=“a”top=“5”left=“5”width=“180”height=“5”/>]) surrounded by [<layout>] and [</layout>] indicates that the content is displayed upon a display screen of the reception terminal apparatus 23 as described below. In other words, on the display screen, the multimedia content specified by [region id=“a”] is displayed at a position of 5 pixels from the top and 5 pixels from the left, and with a width of 180 pixels and height of 180 pixels.
In FIG. 2, the portion surrounded by the first pair of [<par dur=“10 s”>] and [</par>] represents such apparatus that distributes the above content during the first ten seconds of content distribution.
“<audio src=rstp://haisen-souchi-103/content-A-1.mp4/>” indicates the following in FIG. 2. Namely, an apparatus that has a Uniform Resource Locator (URL) referred to as [rstp://haisen-souchi-103/content-A-1.mp4] distributes audio data. The URL indicates that a content distribution apparatus referred to as [haisen-souchi-103] distributes the content referred to as [content-A-1.mp4] using a session control protocol called Real Time Streaming Protocol (RTSP).
“<video src=“rtsp://haisen-souchi-103/content-V-1.mp4” region =“a”/>” shown in FIG. 2 indicates that the content distribution apparatus referred to as [haisen-souchi-103] distributes the content referred to as [content-A-1.mp4] using RTSP. On the other hand, in FIG. 2, the portion surrounded by the second pair of [<par dur=“10 s”>] and [</par>] represents such apparatus that distributes the above content between the tenth second from starting content distribution and the twentieth second from starting content distribution. In FIG. 2, the portion surrounded by the third pair of [<par dur=“10 s”>] and [</par>] represents such apparatus that distributes the above content between the twentieth second from starting content distribution and the thirtieth second from starting content distribution.
The description of the operations of a conventional distribution system is provided as follows. FIG. 3 is a sequence diagram showing the operations of the conventional distribution system.
In step S1100, the reception terminal apparatus 23 transmits a request for multimedia content description data concerning a predetermined multimedia contents (such as, musical contents) to a distribution apparatus.
In step S1110, the first distribution apparatus 21 transmits the multimedia content description data (such as, SMIL data) corresponding to the predetermined multimedia contents to the reception terminal apparatus 23. For example, the a predetermined multimedia contents are assumed to be stored in the second distribution apparatus 22.
In step S1120, transmission control processing for the multimedia contents is executed according to RTSP between the reception terminal apparatus 23 and the second distribution apparatus 22. For example, the exchange of data concerning the data transmission method between the reception terminal apparatus 23 and the second distribution apparatus 22 is executed according to RTSP. Then, a connection between the reception terminal apparatus 23 and the second distribution apparatus 22 is established, and the data transmission method is determined.
In step S1130, the second distribution apparatus 22 transmits the predetermined multimedia contents to the reception terminal apparatus 23 according to the determined transmission method. Transmission of the multimedia contents is processed with Real-time Transport Protocol (RTP).
In this manner, when the reception terminal apparatus 23 transmits a request for a predetermined multimedia contents to the SMIL data distribution apparatus 21, the predetermined distribution apparatus 22 then transmits the above multimedia contents to the reception terminal apparatus 23.
However, the conventional technology has the following problems. In the case where the reception terminal apparatus 23 obtains contents from a distribution apparatus located at a distance over the network, a large amount of network resources are consumed in content distribution. In such case, for example, at least one of network congestion, decrease in transmission bit rate, or bit error occurs. As a result, there is the problem of content distribution quality decreasing.
Conventionally, there is the technology of locating a cache apparatus on the network. In this conventional technology, a cache apparatus located near the reception terminal apparatus 23 temporarily stores contents. Then, the reception terminal apparatus 23 is able to obtain the contents from the cache apparatus.
By this means, the reception terminal apparatus 23 can access the cache apparatus located near by rather than the distribution apparatus located at a distance over the network. As a result, the response time for the request of the reception terminal apparatus may be reduced. Furthermore, consumption of network resources may be reduced. Furthermore, occurrence of network congestion as well as the decrease in data quality due to bit error may be controlled.
The distribution system that utilizes such cache apparatus includes for example, the conventional technology as described below.
“A cache apparatus that determines whether or not storage of data is performed according to priority of data” is disclosed in the prior art of Japanese Patent Application Laid-Open No. 2000-209258. The following technology is disclosed in the prior art of Japanese Patent Application Laid-Open No. 2000-250803. A cache apparatus pre-fetches a Web page with a high jump probability among Web pages linked to a WWW page. The cache apparatus then quickly transmits a response for the Web page request to the reception terminal apparatus.
In the prior art of Japanese Patent Application Laid-Open No. 2000-276425, in the case where the reception terminal apparatus moves, the cache apparatus that is close to the reception terminal apparatus pre-fetches contents before the content request is transmitted from the reception terminal apparatus.
The following technology is disclosed in the prior art of Japanese Patent Application Laid-Open No. 2000-293424. When the cache apparatus stores data and transmits data to the reception terminal apparatus, the cache apparatus performs operations for storing data independent from the operations of transmitting data to the reception terminal apparatus 7. Accordingly, the operations of storing data in the cache apparatus may be stably performed.
In the prior art of Japanese Patent Application Laid-Open No. 2001-202330, several cache apparatus store the same data. Thus, even if one cache apparatus can not perform data distribution, another cache apparatus may perform data distribution.
However, the conventional technology had the following problems. Conventionally, the reception terminal apparatus was only able to access cache apparatus that were already registered in the reception terminal apparatus. Thus, cache apparatus that were inaccessible to the reception terminal apparatus existed among the cache apparatus linked to the network. As a result, since cache apparatus exist that the reception terminal apparatus could not access utilized, network resources were not fully utilized.
Furthermore, even if a cache apparatus that the reception terminal apparatus could quickly access was linked to the network, in the case where such cache apparatus had not been registered in the reception terminal apparatus, there were problems such as described below. Since the cache apparatus was inaccessible to the reception terminal apparatus, reducing the access time of the reception terminal apparatus was not possible. As a result, network congestion occurred, as well as improvements in content distribution quality being insufficient.